Portable devices such as laptop computers, cell phones, personal digital assistants, and the like, are becoming more common nowadays as the capabilities and utilities of such devices continue to expand. Many portable electronic devices are powered by a rechargeable battery, e.g., lithium, nickel-cadmium, or nickel-metal hydride type batteries, to facilitate the portable nature of such devices. Such portable electronic devices may also be powered by a DC (direct-current) power source when the situation permits, e.g., an AC/DC adapter is plugged into a conventional AC (alternating current) outlet. The DC power source may also provide power to recharge the rechargeable battery cells in a battery charging mode. In the battery charging mode, rechargeable battery cells are protected to avoid an over-voltage condition which may lead to cell burning.
FIG. 1 shows a block diagram of conventional detection circuitry 100 providing over-voltage protection (OVP) (hereinafter, OVP circuitry 100) for rechargeable battery cells. In the conventional OVP circuitry 100, a sense resistor string including resistors R11 and R12 is used to sense a voltage of a rechargeable battery cell 101. A voltage reference unit 103 provides a fixed reference voltage VREF to be compared with the sensed voltage VSEN via a comparator 105. The comparator 105 generates an output signal OVP if an over-voltage condition is present. When the sensed voltage VSEN is lower than the reference voltage VREF, the output signal OVP is logic low, indicating that the cell voltage of the cell 101 is in a normal range. When the sensed voltage VSEN is higher than the reference voltage VREF, the output signal OVP is logic high, indicating the occurrence of an over-voltage condition in the cell 101.
As shown in FIG. 1, the conventional OVP circuitry 100 has three DC current branches: a voltage reference unit branch, a sense resistor string branch and a comparator branch. The power consumption of these three DC current branches can be quite high; thus, the performance of the circuitry is inefficient. A circuit that addresses this shortcoming would be beneficial.